I recently changed the lcd screen of my Dell Studio XPS 1340 because it broke.
I got the same screen model I had and replaced it and the screen and the computer seem to be working pretty well. There is however a very high pitched low volume noise very much like a dog whistle coming from the ccfl cables or the inverter but I am most positive that it is coming from the ccfl cables of the lcd screen. I had to follow this tutorial (http://www.blisscomputers.net/changing-extending-ccfl-c...) to extend the ccfl cables as they were too short. I did this twice, the second time to try to make the connection between the cables better as I thought the noise might be coming from there. I am not sure what could be causing this sound or how I could fix it. Thank you!
its the high frequency power inverter that runs the ccfl. With the display opened for access use something nonconductive to press around and see if you can quiet it up. its probably the board or a coil on the board, but could travel down the wires. Once you find it a little hotglue will quiet it right up.
I ended up receiving a replacement screen from the company that sold me the LCD screen so now my screen is working fine. There is a way to replace the ccfl cables and there are tutorials online (http://www.laptoprepair101.com/laptop/2007/12/09/replac...) but it is a lot harder than replacing the lcd screen because you could much more easily break something. For those who are having a problem with ccfl cable length, I recommend getting an extension cable for the ccfl instead of trying to cut the wires. The problem was I think that there was an excess or lack of enough power or electricity flowing through the cables since I cut them and probably left less internal wires than there were originally. The company I bought the screen from where super helpful, I really recommend them http://www.blisscomputers.net/